Detection and display device

ABSTRACT

A device for detecting and displaying the relative position of a generally horizontal reference plane of light. even when partial shading of the device occures, includes a photodetector means having including first and second interdigitated photodetector elements positioned adjacent each other on the device. The first and second interdigitated photodetector element provide first and second detection signals, respectively. A circuit means, responsive to the photodetector means, for determines the relative levels of the first and second detection signals such that the position of the reference plane of light with respect to the detector device is determined. A display means, responsive to the circuit means, for provides an indication of the position of the referece plane of light with respect to the detector device.

BACKGROUND OF THE INVENTION

The present invention relates to equipment of the type used in surveyingand construction and, more particularly, to a detector device for suchan application which detects the position or level of a reference planedefined by a rotating laser beam or defined by a stationary plane oflaser light.

Laser systems have been employed in surveying and construction in whicha laser beam is rotated in either a horizontal or a graded plane. U.S.Pat. No. 4,062,634, issued Dec. 13, 1977, to Rando, illustrates a laserprojector device which provides such a rotating reference beam. Therotating beam defines a plane, and various measurements can be madeusing the plane as a reference. For example, the elevation of a pointremote from the laser beam projector device may be measured by means ofa rod on which a laser beam detector is mounted. The bottom of the rodrests on the ground at the point where the measurement is to be made,and the operator moves the detector along the rod to a position where itintercepts the laser beam, as indicated by a meter or other display onthe detector device. One such detector device is shown in U.S. Pat. No.4,240,208, issued Dec. 23, 1980, to Pehrson.

A similar surveying system is shown in U.S. Pat. No. 4,732,471, issuedMar. 22, 1988, to Cain et al. In the Cain et al system, a rotating beamis not used. Rather, a laser transmitter produces an alignment field byprojecting laser energy in a non-planar, stationary reference cone. Whenthe transmitter is level, this reference cone declines from thehorizontal in a amount sufficient so that some compensation is providedfor positional errors which occur due to the curvature of the earth. TheCain et al patent discloses a small, hand-held device which includes adisplay and a photodetector module.

Both of the detector devices shown in the Cain et al and Petersenpatents include a pair of adjacent, triangularly shaped photodetectorelements. The orientation of the photodetector elements is such that thechanges in the signal outputs from the elements which occur due tomovement of the light are inversely related. As the reference lightmoves upward, the signal output from one of the elements increases whilethe signal output from the other of the elements decreases. The oppositesignal changes occur when the position of the reference light movesdownward. Naturally, the signal levels are also affected by theintensity of the light source and the distance of the photodetectorelements from the light source. By comparing the relative signal outputlevels from the two photodetector elements, however, it is possible toobtain an indication of the position of the reference light withoutregard to the absolute intensity of the light.

While such a detector arrangement provides accurate operation undervarying conditions, it has been found to be subject to error ininstances when the detector device is improperly oriented. Thephotodetector elements are positioned behind an aperture in the case ofthe detector device. If the detector device is misaligned by rotationabout a vertical axis such that the light does not strike the elementsat normal incidence, shading of the elements by the case at the edge ofthe aperture can occur. If the angle of incidence is large, thephotodetector elements may be entirely shaded and the device will notfunction. This is an inconvenience for the operator, but is simplycorrected by realignment of the device. More serious, however, is thesituation in which the photodetector elements are only partially shaded.In this event, the two elements are not shaded equally, therebyproducing a shift in the relative signal levels from the elements, and acorresponding error in the detected position of the reference light.Since the device provides an indication of light position, the operatormay be unaware of the misalignment of the device and the resulting errorin its operation.

Accordingly, it is seen that there is a need for an improved device fordetecting and displaying the relative position of reference light whichis less sensitive to misalignment of the device.

SUMMARY OF THE INVENTION

This need is met by a device according to the present invention fordetecting and displaying the relative position of a generally horizontalreference plane of light, even when partial shading of the deviceoccurs. The device includes photodetector means having first and secondinterdigitated photodetector elements positioned adjacent each other onthe device. The first and second interdigitated photodetector elementsprovide first and second detection signals, respectively. The deviceincludes circuit means, responsive to the photodetector means, fordetermining the relative levels of the first and second detectionsignals such that the position of the reference plane of light withrespect to the detector device is determined. Finally, the deviceincludes display means, responsive to the circuit means, for providingan indication of the position of the reference plane of light withrespect to the detector device.

The first photodetector element comprises a plurality of sectionsarranged in a generally vertically oriented row. The secondphotodetector element comprises a plurality of sections, each section ofthe second photodetector element being positioned between adjacentsections of the first photodetector element. The heights of the sectionsof the first photodetector element increase from the bottom to the topof the row, and the heights of the sections of the second photodetectorelement decrease from the bottom of the top of the row.

The sum of the height of a section of the first photodetector elementand the height of the section of the second photodetector elementdirectly therebeneath remains constant along the row. The sum of theheight of a section of the first photodetector element and the height ofthe section of the second photodetector element directly therebeneath ispreferably no greater than approximately one-half the vertical thicknessof the reference plane of light.

A device for detecting the relative position of a reference plane oflight, the operation of the device being unaffected by partial shadingof the device, comprises a first photodetector element including aplurality of sections arranged in a row which is generally perpendicularto the reference plane of light; a second photodetector elementincluding a plurality of sections arranged along the row, each sectionof the second photodetector element being positioned between adjacentsections of the first photodetector element; and circuit means,responsive to the first and second photodetector elements, fordetermining the relative levels of the first and second detectionsignals such that the position of the reference plane of light withrespect to the detector device is determined.

The dimensions in a direction parallel to the row of the sections of thefirst photodetector element increase from a first end to a second end ofthe row, and the dimensions in a direction parallel to the row of thesections of the second photodetector element decrease from the first endto the second end of the row. The sum of the dimension in a directionparallel to the row of a section of the first photodetector element andthe dimension in a direction parallel to the row of the section of thesecond photodetector element directly thereadjacent remains constantalong the row. The sum of the dimension in a direction parallel to therow of a section of the first photodetector element and the dimension ina direction parallel to the row of the section of the secondphotodetector element directly thereadjacent is no greater thanapproximately one-half the thickness of the reference plane of light.

Accordingly, it is an object of the present invention to prvoide animproved device for detecting and displaying the position of a plane oflight; to provide such a device in which the partial shading of thedevice does not adversely affect the position detected and displayed;and to provide such a device in which a photodetector means includes apair of interdigitated photodetector elements.

Other objects and advantages of the invention will be apparent from thefollowing description, the accompanying drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a detector device according to thepresent invention;

FIG. 2 illustrates a prior art configuration of photodetector elements;

FIG. 3 is an enlarged view with portions broken away, illustratinginterdigitated photodetector elements according to the presentinvention; and

FIG. 4 is a block diagram of the circuitry of the detector device of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference is made to FIGS. 1 and 4, which generally illustrate adetection and display device 10 according to the present invention. Thedevice detects reference light and provides an indication of thelocation of the reference light with respect to the device. It is to beunderstood that the device 10 may be used with transmitters whichprovide either a stationary plane or field of light, or a rotating beamof light. Additionally, the light may be projected in a true plane, orin a conical shape or other shape to define a reference. Reference lightmay, for example, be produced by a device such as shown in U.S. Pat. No.4,062,634, issued Dec. 13, 1977, to Rando et al, or by a device such asshown in U.S. Pat. No. 4,732,471, issued Mar. 22, 1988, to Cain et al,both of which are discussed above.

The detector device 10 includes a display 12, and a photodetector means14 positioned in a window or aperture 16 defined by case 18. Thedetector device 10 is switched on by control knob 20 and then positionedat the approximate height of the reference light. The light strikes thephotodetector means 14, and a circuit means including detectioncircuitry 22, provides an indication on display 12 of the position ofthe reference plane of light with respect to the detector device.Specifically, the display 12 indicates whether the light is above,below, or within a reference band which is centered between the top andbottom of the photodetector means 14. (Although this discussion may makereference to the top or bottom of the device or a component, or to ahorizontal orientation or a vertical orientation, it will be appreciatedthat these terms are presented as relative to each other, for ease ofexplanation and understanding, and that they are in no way intended tobe limited to absolute orientations.)

The detection circuitry 22 is responsive to the photodetector means 14for determining the relative levels of the first and second detectionsignals on lines 23 and 24, respectively, such that the position of thereference light is determined. The display 12, which may for example bean LCD display, includes a pair of arrows 25 and 26, and a bar 28. Arrow25 and arrow 26 are displayed if the beam is below or above thereference band. Bar 28 is displayed if the beam is within the band.Additionally, the display may provide an indication as to whether thelight is above, below, or within a second, larger reference band, whichis aligned with the first reference band. The details of the detectioncircuitry 22 by which this may be accomplished are described in theabove identified Cain et al patent.

As discussed above, prior art detection devices have utilized a pair ofdetection elements, each configured in a triangular shape, andpositioned such that movement of the reference light vertically causesan increase in the output signal from one of the detection elementswhile at the same time causing an increase in the output signal from theother of the detection elements. This arrangement is illustrated in FIG.2.

The elements 30 and 32 are positioned to intercept a plane of light 34.It will be appreciated that the level of the output signal from anelement is directly related to the area of the element which isilluminated. As a consequence, movement of the light 34 upward increasesthe output signal from element 30 on line 23' and decreases the outputsignal from element 32 on line 24', while movement of the light 34downward decreases the output signal from element 30 and increases theoutput signal from element 32.

When the detection device is misaligned by rotation about its verticalaxis, a portion of the photodetector elements may be shaded from thelight 34 by the case 18 at the side of the aperture 16. This results inlight being blocked from hatched area 36. It will be apparent thatelement 30 will provide a higher level output signal in this situationthan element 32, since a larger area of element 30 remains illuminated.As a consequence, the light 34 will be indicated as being higher than isactually the case. Since the device does provide an output, however, theoperator may be unaware of this error.

This problem is eliminated by the photodetector means 14 of the presentinvention, illustrated in FIG. 3. The photodetector means 14 includesfirst and second interdigitated photodetector elements 38 and 40,positioned adjacent each other on the device. The first and secondinterdigitated photodetector elements 38 and 40 provide first and seconddetection signals on lines 23 and 24, respectively. The firstphotodetector element 38 is made up of a plurality of separate sectionswhich are arranged in a generally vertically oriented row andelectrically conencted to line 23. Similarly, the second photodetectorelement 40 is made up of a plurality of sections which are electricallyconnected to line 24. Each section of the second photodetector element40 is positioned between adjacent sections of the first photodetectorelement 38.

As is apparent from FIG. 3, the heights of the sections of the firstphotodetector element 38 increase from the bottom to the top of the row,and the heights of the sections of the second photodetector element 40decrease from the bottom to the top of the row. This arrangement isprovided so that the sum h of the height of a section of the firstphotodetector element 38 and the height of the section of the secondphotodetector element 40 directly therebeneath remains constant alongthe row.

As a consequence, it will be appreciated that relative levels of theoutput signals on lines 23 and 24 will provide an indication of the areawhich is illuminated along the row of element sections. If the lightstrikes the photodetector elements near the middle of the row, the twosignal levels on lines 23 and 24 will be approximately equal.Illumination of the elements at the upper part of the row produces ahigher level signal on lines 23, whereas illumination of the elements atthe lower part of the row produces a higher level signal on line 24. Ifthe device is misaligned by rotation about a vertical axis to a degreesufficient to produce shading of the type illustrated in FIG. 2, boththe first and second detection signals on lines 23 and 24 are reduced inamplitude. The relationship between these signals remains the same,however, since the relationship between the illuminated areas of the twointerdigitated photodetector elements is unchanged.

Preferably, the sum h of the height of a section of the firstphotodetector element 38 and the height of the section of the secondphotodetector element 40 directly therebeneath is no greater thanapproximately one-half the vertical thickness of the reference plane oflight. It will be appreciated that this ensures that enough of thesections of both elements are illuminated that the desired relationshipbetween the first and second detection signals is obtained.

Having described the invention in detail and by reference to thepreferred embodiment thereof, it will be apparent that othermodifications and variations are possible without departing from thescope of the invention defined in the appended claims.

What is claimed is:
 1. A device for detecting and displaying therelative position of a generally horizontal reference plane of light,even when partial shading of said device occurs,comprising:photodetector means, including first and secondinterdigitated photodetector elements positioned adjacent each other onsaid device, said first and second interdigitated photodetector elementsproviding first and second detection signals, respectively, circuitmeans, responsive to said photodetector means, for determining therelative levels of said first and second detection signals such that theposition of said reference plane of light with respect to said detectordevice is determined, and display means, responsive to said circuitmeans, for providing an indication of the position of said referenceplane of light with respect to said detector device.
 2. The device ofclaim 1 for detecting and displaying the relative position of agenerally horizontal reference plane of light, in which said firstphotodetector element comprises a plurality of sections arranged in agenerally vertically oriented row, and in which said secondphotodetector element comprises a plurality of sections, each section ofsaid second photodetector element being positioned between adjacentsections of said first photodetector element.
 3. The device of claim 2for detecting and displaying the relative position of a generallyhorizontal reference plane of light, in which the heights of saidsections of said first photodetector element increase from the bottom tothe top of said row, and in which the heights of said sections of saidsecond photodetector element decrease from the bottom to the top of saidrow.
 4. The device of claim 3 for detecting and displaying the relativeposition of a generally horizontal reference plane of light, in whichsum of the height of a section of said first photodetector element andthe height of the section of said second photodetector element directlytherebeneath remains constant along said row.
 5. The device of claim 4for detecting and displaying the relative position of a generallyhorizontal reference plane of light, in which said sum of the height ofa section of said first photodetector element and the height of thesection of said second photodetector element directly therebeneath is nogreather than approximately one-half the vertical thickness of saidreference plane of light.
 6. A device for detecting the relativeposition of a reference plane of light, the operation of said devicebeing unaffected by partial shading of said device, comprising:a firstphotodetector element including a plurality of sections arranged in arow which is generally perpendicular to said reference plane of light, asecond photodetector element including a plurality of sections arrangedalong said row, each section of said second photodetector element beingpositioned between adjacent sections of said first photodetectorelement, and circuit means, responsive to said first and secondphotodetector elements, for determining the relative levels of saidfirst and second detection signals such that the position of saidreference plane of light with respect to said detector device isdetermined.
 7. The device of claim 6 for detecting the relative positionof a reference plane of light, in which the dimensions in a directionparallel to said row of said sections of said first photodetectorelement increase from a first end to a second end of said row, and inwhich the dimensions in a direction parallel to said row of saidsections of said second photodetector element decrease from said firstend to said second end of said row.
 8. The device of claim 7 fordetecting the relative position of a reference plane of light, in whichthe sum of the dimension in a direction parallel to said row of asection of said first photodetector element and the dimension in adirection parallel to said row of the section of said secondphotodetector element directly thereadjacent remains constant along saidrow.
 9. The device of claim 8 for detecting the relative position of areference plane of light, in which the sum of the dimension in adirection parallel to said row of a section of said first photodetectorelement and the dimension in a direction parallel to said row of thesection of said second photodetector element directly thereadjacent isno greater than approximately one-half the thickness of said referenceplane of light.